Medical instruments have traditionally been sterilized using heat, for example steam, or a chemical, such as formaldehyde or ethylene oxide in the gas or vapor state. Both heat and chemical sterilization have drawbacks. For example, many medical devices, such as fiberoptic devices, endoscopes, power tools, etc. are sensitive to heat, moisture, or both.
Formaldehyde and ethylene oxide are both toxic gases which pose a potential hazard to health workers. After sterilization with ethylene oxide, the articles require long aeration times to remove the gas from articles which have been sterilized. This makes the sterilization cycle time undesirably long.
Sterilization using liquid hydrogen peroxide solutions has been found to require a high concentration of sterilant, extended exposure times and/or elevated temperatures. However, sterilization using hydrogen peroxide vapor has been shown to have some advantages over other chemical sterilization processes (see, for example, U.S. Pat. Nos. 4,169,123 and 4,169,124). The combination of hydrogen peroxide vapor and a plasma provides additional advantages, as disclosed in U.S. Pat. No. 4,643,876. U.S. Pat. 4,756,882 discloses the use of hydrogen peroxide vapor, generated from an aqueous solution of hydrogen peroxide, as a precursor of the reactive species generated by a plasma generator. The combination of hydrogen peroxide vapor in close proximity with the article to be sterilized and plasma acts to sterilize the articles, even in closed packages.
Effective sterilization of articles with hydrogen peroxide vapor, either with or without plasma, requires a certain minimum concentration of hydrogen peroxide vapor. If not enough hydrogen peroxide vapor is present, the article will not be sterilized.
If too much hydrogen peroxide is used, the hydrogen peroxide vapor can potentially damage the medical devices, particularly if they contain nylon, neoprene, brass or copper. For hydrogen peroxide absorbent materials, too much peroxide may leave an unacceptable residue on the medical device that may be incompatible with the user or patient. In addition, the use of too much hydrogen peroxide increases the cost of sterilization.
The determination of the appropriate amount of peroxide is especially important for large sterilizers, because the load in large sterilizers can vary more than the load in small sterilizers. One cannot assume the worst-case scenario for each cycle and introduce the maximum possible amount of sterilant. Therefore, there is a need for a method for determining how much hydrogen peroxide is needed to effectively sterilize the medical device without damaging it or leaving too much residual.
There is a need for determining the load of equipment to be sterilized in the sterilization chamber in order to obtain the best efficiency and material compatibility